1. Field of the Invention
The invention relates to new and improved catalysts comprising metallic palladium and gold, which are useful for the production of vinyl acetate by reaction of ethylene, oxygen and acetic acid.
2. Description of the Related Art
It is known to produce vinyl acetate by reaction of ethylene, oxygen and acetic acid using a catalyst comprising palladium and gold, supported on a carrier. While the process utilizing such a catalyst is capable of producing vinyl acetate at relatively high levels of productivity, any expedient which could possibly result in even greater productivity or a decrease in by products would be very desirable.
The following references may be considered material to the invention claimed herein.
U.S. Pat. No. 3,775,342 issued Nov. 27, 1973, and U.S. Pat. No. 3,822,308 issued Jul. 2, 1974, both to Kronig et al., each discloses a method of making vinyl acetate catalysts comprising treating a support simultaneously or successively with a solution A containing dissolved salts of noble metals such as palladium and gold and a solution B containing compounds able to react on the support with the noble metal salts to form water-insoluble compounds, treating such water-insoluble compounds with a reducing agent to convert the water-insoluble noble metal compounds to the free metals, washing the catalyst to remove water-soluble compounds, and applying an alkali metal compound, e.g., an alkali metal carboxylate before or after treatment with the reducing agent. Solution A can optionally also contain salts of other metals such as magnesium, calcium, barium and copper.
U.S. Pat. No. 5,322,710, issued Jul. 26, 1994, to Nicolau et al., discloses a method of preparing a catalyst useful for the production of vinyl acetate by reaction of ethylene, oxygen and acetic acid, comprising impregnating a porous support with water soluble salts of palladium and gold, fixing the palladium and gold as insoluble compounds on the support by immersing and tumbling the impregnated support in a reactive solution for at least 1/2 hour to precipitate such compounds, and subsequently reducing the compounds to free metallic form.
U.S. Pat. No. 5,347,046, issued Sept. 13, 1994 to White et al., discloses catalysts for the production of vinyl acetate by reaction of ethylene, oxygen, and acetic acid, comprising a palladium group metal and/or a compound thereof, gold and/or a compound thereof, and copper, nickel, cobalt, iron, manganese, lead or silver, or a compound thereof, preferably deposited on a support material.
Suslick, K. S., "Organometallic Sonochemistry," Advances in Organometallic Chemistry 25, 73-119 (1986) is a general article on the application of ultrasound waves to organometalic reactions.
Suslick, K. S.; Fang, M.; Hyeon, T.; and Cichowlas, A. A., "Nanostructured Fe-Co Catalysts Generated by Ultrasound," Materials Research Society Symposia Proceedings, 351, 443-448 (1994), discuss the preparation and activity of Fe-Co catalysts generated with ultrasound waves.
Okitsu, K.; Bandow, H.; and Maeda, Y.; "Sonochemical Preparation of Ultrafine Palladium Particles," Chemistry of Materials 8, 315-317 (1996) discuss the sonochemical reduction of Pd (II) in the presence of protective agents such as surfactants to produce ultrafine Pd particles and state that colloidal dispersion of these particles "exhibit interesting catalytic activity."